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What is an antacid?

Dr. Lawrence S. Friedman, MD
Gastroenterologist

Antacids are inexpensive over-the-counter remedies that neutralize digestive acids in the stomach and esophagus, at least in mild cases of heartburn. While many people find tablets more convenient, liquids provide faster relief. Tablets must be chewed thoroughly in order to be effective. The best time to take an antacid is after a meal or when symptoms occur. The usual recommended dosage is 1 to 2 tablespoons each time.

There are three basic salts used in antacids: magnesium, aluminum, and calcium. A major side effect of magnesium hydroxide is diarrhea, while the most common side effect of antacids containing aluminum hydroxide is constipation.

Antacids high in calcium (Tums, Rolaids, Titralac, and Alka-2) are probably the strongest. Calcium carbonate products have been used for centuries in the form of chalk powder and ground oyster shell. They, too, can be constipating if consumed in sufficient quantities.

Sodium bicarbonate, or baking soda, which is less powerful than other antacids, is the active ingredient in many seltzer antacids (Alka-Seltzer, Bromo-Seltzer) and is present in mineral water.

Because no single agent is perfect, many antacids combine several ingredients that are designed to balance their respective side effects.

Donna Hill Howes, RN
Family Practitioner

Antacids neutralize acid in the stomach. They act quickly and for a short period of time. This makes them useful for as-needed treatment of mild acid reflux symptoms such as occasional heartburn. Antacids are generally available without a prescription. They are less effective than proton pump inhibitors, and are not meant for long-term continuous treatment of GERD. They do not heal damage to the esophagus that has been caused by acid.

A number of compounds and combinations are used as antacids. The most common ingredients are aluminum, magnesium, calcium carbonate, and sodium bicarbonate. Combinations of aluminum and magnesium are found in many products, such as Gaviscon, Maalox, Di-Gel, and Mygel. Calcium carbonate and magnesium are combined in products such as Rolaids and Mylanta. Sodium bicarbonate is an active ingredient in Alka-Seltzer. Calcium carbonate is the active ingredient in Tums. A chemical called alginate, which is derived from seaweed, is combined with an antacid in some products, such as certain formulations of Gaviscon. Alginate reacts with stomach acid to form a barrier that helps prevent the reflux of acid from the stomach into the lower esophagus. The combination of an antacid and alginate appears to prevent reflux more consistently than an antacid alone.

You should see your doctor if you are needing to take antacids frequently or if your symptoms do not improve with antacids. 

This answer was adapted from Sharecare's award-winning AskMD app. Start a consultation now to find out what's causing your symptoms, learn how to manage a condition, or find a doctor.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.